FIGS. 10 through 13 show a rotary encoder of the prior art. FIGS. 10 and 11 show a single-shaft type rotary encoder, where FIG. 10 is a sectional side view and FIG. 11 is a plan view of a circular comb-shaped contact. In FIGS. 10 and 11, reference numeral 1 denotes a base member made from die cast zinc or other material. On the center of the upper surface of the base member, there is provided is a cylindrical bearing 2 in which the operating shaft 3 is fitted and supported rotatably and on which a screw thread 2' for attachment to a device is provided. The operating shaft 3 comprises a fitting portion 3' and an attachment portion 3" above the fitting portion 3' for attachment to a control knob 4. At the lower end of the operating shaft 3, a rotary contact plate 6 made from an insulating resin and having a circular comb-shaped movable contact 5 on its lower surface is supported. A fixed contact substrate 8 made from an insulating resin is attached to the lower end of a cylindrical wall 7 extending down from the outer circumference of the base member 1, and contact portions of flexible fixed contacts 9 protruding up from the fixed contact substrate 8 are in flexible contact with the circular comb-shaped movable contact 5 on the above-mentioned rotary contact plate 6.
Therefore, by rotating the operating shaft 3 via the control knob 4, a pulse signal is generated between the circular comb-shaped movable contact 5 and the flexible fixed contacts 9 and output to an external connection terminal 10 with which the fixed contacts 9 have continuity.
The rotary encoder of this type is usually provided with a control knob having a wide diameter on the operating shaft to facilitate fast rotation, but in order for the control knob to turn smoothly, the knob must be attached to the operating shaft without inclination and there must be as little play as possible in the fitting portion of the operating shaft and the shaft supporting portion. In order to minimize any inclination in the attachment portion of the control knob and play in the fitting portion of the operating shaft, the attachment portion and the fitting portion must be made as long as possible.
However, in the configuration of the abovementioned conventional rotary encoder, the length A of the attachment portion of the control knob 4 to the operating shaft 3, and the length B of the fitting portion of the operating shaft 3 to the bearing 2 both extend above the height C of the rotary encoder base member 1. Therefore, to make the lengths A and B longer means to make the overall height (A+B+C) of the rotary encoder longer.
FIGS. 12 and 13 show a double-shaft rotary encoder wherein the outer shaft generates a speed mode switching signal for fast forwarding a video tape and the inner shaft generates a pulse signal for frame advance of a video tape. FIG. 12 is a sectional side view of the double-shaft rotary encoder and FIG. 13 is a plan view of a fixed contacts of the same.
In FIGS. 11 and 12, reference numeral 21 denotes a base member made from die cast zinc or other material. On the center of the upper surface of the base member, there provided is a cylindrical bearing 22 in which an outer operating shaft 23 is fitted and supported rotatably and on which a screw thread 22' for attachment to a device is provided. The outer operating shaft 23 is made from an insulating resin and comprises a cylindrical fitting portion 23' and an attachment portion 23" extending above the fitting portion for attachment to a control knob, and at the lower end of the outer shaft 23, an outer contact substrate 26 supporting outer rotary flexible contacts 25 is formed into a single unit with the outer operating shaft 23. An inner operating shaft 27 supported in the center hole of the outer operating shaft 23 so that it can independently rotate comprises an attachment portion 27' on its extended portion for attachment to an inner control knob 28. Also, at the lower end of the inner operating shaft 27, an inner contact substrate 30 which is made from an insulating material and supports inner rotary flexible contacts 29 is attached so that it rotates together with the inner operating shaft 27 and is positioned vertically by two washers 31 and 32.
A contact substrate 36 made from an insulating material and having a plurality of concentric fixed contacts 34 and 34', and 35 and 35' on its upper surface is attached to the lower end of a cylindrical wall 33 extending down from the outer circumference of the base member 21. The outer rotary flexible contacts 25 protruding from the outer contact substrate 26 and the inner rotary flexible contacts 29 protruding from the inner contact substrate 30 are in contact with the fixed contacts 34 and 34', and 35 and 35', respectively. In FIG. 13, the hatched portions denote the fixed contacts 34 and 34', and 35 and 35' exposed on the surface, and the solid portions denote leads to the terminals covered by an insulating film. When the outer operating shaft 33 is turned by the outer control knob 24, a speed mode switching signal for fast forwarding of the video tape is generated between the outer rotary flexible contacts 25 and the fixed contacts 34 and 34'. Likewise, when the inner operating shaft 27 is turned by the inner control knob 28, a pulse signal is generated between the inner rotary flexible contacts 29 and the fixed contacts 35 and 35', which in turn generates a signal for frame advance of the video tape. These signals are output from the terminals 37 and 38 connected to the respective fixed contacts.
However, in the single-shaft rotary encoder shown in FIGS. 10 and 11, it is difficult to decrease the overall height of the rotary encoder as mentioned above, and rotary encoders with this conventional configuration are not suited to current compact, high-performance devices.
In addition to the problems of the single-shaft rotary encoder above, in the double-shaft rotary encoder shown in FIGS. 12 and 13, the cylindrical outer operating shaft 23 is supported by the cylindrical bearing 22 on the upper surface of the base member 21 and the inner operating shaft 27 is supported within the center hole of the outer operating shaft 23, so that the frequently used inner operating shaft 27 has a large amount of play in the radial direction (radial play) due to the gaps both between the bearing 22 and the outer operating shaft 23, and between the outer operating shaft 23 and the inner operating shaft 27. Also, when the above two gaps are made small so as to reduce radial play, other problems are caused such that the rotating torque may increase, and the outer operating shaft 23 and inner operating shaft 27 may rotate together.